Fibre Channel (“FC”) network is a no-drop network that operates on a credit-based flow control mechanism for communication between any pair of ports. A buffer-to-buffer (“B2B”) credit number for a peer port tracks the number of packet buffers available on a peer port for packet transmission toward that port. An FC packet may be transmitted by a port only if it has B2B credit for the peer port that is greater than zero. A packet transmitted from a port decrements the B2B credit counter of that port. An acknowledgement of completion of processing of a packet takes the form of a Receiver Ready (“R_RDY”) primitive signal from the peer port, which increments the B2B credit counter. The R_RDY primitive only contains information that a buffer is available at the port sending R_RDY and no other information. The B2B counter associated with the transmit buffer of a switch is referred to as a TX_B2B counter and the B2B counter associated with the receive buffer of a switch is referred to as an RX_B2B counter.
A “slow drain device” (or simply “slow device,” as used herein) is a device that does not accept frames at the rate generated by a source; i.e., the R_RDY signals are delayed in response to the frames. A device is only characterized as a slow drain device in situations in which the slow draining nature of the device impacts other devices in a Storage Area Network (“SAN”). Typical FC networks are designed in an Edge-Core or an Edge-Core-Edge fashion in which server and storage devices are connected to edge switches and the core and edge switches are connected by Inter-Switch Links (“ISLs”). In the presence of slow drain devices, FC networks are likely to run out of switch packet buffers, resulting in switch port credit starvation and potential choking of Inter-Switch Links (“ISLs”). An ISL running out of B2B credits results in traffic flows unrelated to the slow drain/stuck device being impacted, due to head-of-line blocking. A slow drain/stuck device condition can arise due to problems in the server Operating System (“OS”) or host bus adapters (“HBAs”), storage issues, switch misconfigurations (e.g., speed mismatches), among other issues. Many cases involving slow drain devices are due to servers being overwhelmed by large chunks of data being received from a storage device in response to a READ operation from the server. Large storage area network (“SAN”) installations may face this problem on a daily basis and may fence off the ports that are deemed to be slow drain ports (e.g., 25-30 ports per day).